The present invention relates to co-extrusion dies and, in particular, to multiple, coaxial mandrels arranged to provide a layered tube.
It is known to extrude tubing by means of a die having a casing fitted with a mandrel to provide an interspace for extrusion. The mandrel is held in the casing by webs that span between the mandrel and casing to support the mandrel.
It is also known to extrude a tube by means of a spiral groove on a cylinder fitted into a casing. The spiral groove moves the extrudate around the circumference of the cylinder to spread it more evenly and prevent streaking. Eventually, the spiral grooves on the cylindrical surface terminate so that the extrudate is formed into a uniform tube as it exits an annular outlet. Known co-extrusion dies have used a number of nested, spiral-extrusion mandrels. The several resulting layers of extrudate can then be joined at one point to form a multilayer tube. However, the joining of extrudate has not been precisely controlled in the past and therefore irregularities often occur.
It is known to employ an extruder that drives extrudate into a rotator tube to deliver extrudate to a die. Known assemblies for delivering the extrudate to the rotator tube have been configured to allow extrudate to stagnate around its point of delivery to the rotator tube. Consequently, overheating and inconsistent results have resulted from inconsistent delivery times.
Accordingly, there is a need for an improved co-extrusion die and extrusion system for providing multilayered tubes for bags and the like, which avoids the disadvantages of the prior art.